Sharon, Clark Put Spotlight on Stroke

Jan. 5, 2006 -- Only days after stroke-stricken Dick Clark resumed his role as king of New Year's Eve, Israeli Prime Minister Ariel Sharon suffered a devastating stroke just weeks after his first.

Each suffered very different strokes, with very different causes.

How can stroke mean so many different things? Why do different strokes have such different outcomes? For answers to these and other stroke questions, WebMD turned to Keith A. Siller, MD. Siller is medical director of the NYU Comprehensive Stroke Care Center and assistant professor of psychiatry and neurology at the NYU School of Medicine.

Ischemic Strokes

Strokes happen when part of the brain loses its blood supply. This can happen in two major ways.

More than 80% of strokes occur when a blood vessel (an artery) in the brain or neck gets blocked by a blood clot. This is called an ischemic stroke.

"Typical strokes are ischemic and are due to clogged arteries," Siller tells WebMD.

It's not clear which kind of stroke Dick Clark had. But Clark has made public the fact that he has diabetes. People with diabetes tend to have atherosclerosis -- clogged arteries -- so Siller guesses that it is likely Clark suffered an ischemic stroke.

Doctors further classify ischemic strokes by where the blood clot originated. When a clot forms in an artery, stays in place, and blocks the artery, it's called a thrombus -- and a person has a thrombotic stroke. More than half of ischemic strokes are thrombotic strokes.

"Another mechanism of ischemic stroke is a clot arising from the heart: an embolism," Siller says. "That is a clot from one part of the body going to another."

When these traveling clots wedge into a blood vessel leading to the brain, a person has an embolic stroke.

Hemorrhagic Strokes

Strokes also occur when an artery supplying blood to the brain bursts. These are hemorrhagic strokes -- the other major kind of stroke which Sharon most recently suffered.

Hemorrhagic strokes are also further classified by where they originate. When a hemorrhagic stroke happens inside the brain, it's called an intracerebral hemorrhage. When it happens in the subarachnoid space (between the brain and a lining surrounding it), it's called a subarachnoid hemorrhage.

The usual cause of intracerebral hemorrhage is high blood pressure. Another cause is an aneurysm -- a weak spot in the wall of the artery that balloons out. When these balloons pop, a person has a stroke. This is the usual cause of subarachnoid aneurysms.

"Hemorrhagic stroke can be just as devastating as ischemic stroke," Siller says. "And there are other types of bleeding that affect the brain. Subdural hematomas and epidural hematomas are bleeding just outside the brain. Usually caused by a head injury, these are technically not considered strokes. But they do compress the brain and can cause similar disabilities."

How Bad Is a Stroke?

Obviously, a stroke is never a good thing. But some are worse than others. Severity depends on two things: the part of the brain affected and the size of the affected brain area.

"The first distinction in stroke damage is the side of the brain affected," Siller says. "The left side is the dominant hemisphere, related to language function for most people. One of the things people fear the most is a stroke that leaves them unable to speak and to understand speech. When the stroke is on the right, usually patients are able to have normal conversations. There may be more subtle cognitive problems not immediately obvious, but usually right-side stroke patients can have a better recovery."

Sharon's stroke, Siller says, probably was quite large as it required many hours of surgery to drain the blood from his brain. And doctors did not announce which side of the brain was affected.